Understanding and controlling the magnetization dynamics in magnetic multilayers and nanostructures on the femtosecond timescale is becoming indispensable, both at the fundamental level and to develop future technological applications. While direct laser excitation of a ferromagnetic layer was commonly used during the past twenty years, laser-induced hot-electrons femtosecond pulses and subsequent transport in magnetic multilayers have attracted a lot of attention. Indeed, replacing photons by hot-electrons offers complementary information to improve our understanding of ultrafast magnetization dynamics and to provide new possibilities for manipulating the magnetization in a thin layer on the femtosecond timescale.

New study shows elegant mathematical solution to understand how the flow of electrons changes when carbon nanotubes turn into zigzag nanoribbons

In a new study published in EPJ B, Basant Lal Sharma from the Indian Institute of Technology Kanpur provides a detailed analysis of how the flow of heat and electrons is affected at the interface between an ‘armchair’ shaped carbon nanotube and a zigzagging nanoribbon made up of a single-layer carbon honeycomb sheet of graphene. Applications of this method can help us understand the propagation of electrons and thermal flow in graphene and similar materials for electromagnetic devices. For example, a partially unzipped carbon nanotube could act as a device with varying electrical resistance depending on the strength of an external magnetic field applied to it. By contrast, these junctions can also act as perfect ‘valley filters’, allowing certain types of electrons through the junction with the maximum possible conductance, while other electrons can't pass through.

Patchy particles is the name given to a large class of systems of mesoscopic particles characterized by a repulsive core and a discrete number of short-range and highly directional interaction sites. Numerical simulations have contributed significantly to our understanding of the behaviour of patchy particles, but, although simple in principle, advanced simulation techniques are often required to sample the low temperatures and long time-scales associated with their self-assembly behaviour.

In this EPJ E colloquium paper, Rovigatti et al. review the most popular simulation techniques that have been used to study patchy particles, with a special focus on Monte Carlo methods.

A new study shows how to couple highly accurate and simplified models of the same system to extract thermodynamics information using simulations

Computer simulations are used to understand the properties of soft matter - such as liquids, polymers and biomolecules like DNA - which are too complicated to be described by equations. They are often too expensive to simulate in full, given the intensive computational power required. Instead, a helpful strategy is to couple an accurate model - applied in the areas of the system that require greater attention - with a simpler, idealised model. In a recent paper published in EPJ E, Maziar Heidari, from the Max Planck Institute for Polymer Research, Mainz, Germany and colleagues make the accurate model in high-resolution coincide seamlessly with an exactly solvable representation at lower resolution.

A team in China has just calculated the size of scale-free and small-world networks

Networks are often described as trees with spanning branches. How the tree branches out depends on the logic behind the network’s expansion, such as random expansion. However, some aspects of such randomly expanding networks are invariant; in other words, they display the same characteristics, regardless of the network’s scale. As a result, the entire network has the same shape as one or more of its parts. In a new study published in EPJ B, Fei Ma from Northwest Normal University in Lanzhou, Gansu Province, China, anc colleagues calculate the total number of spanning trees in randomly expanding networks. This method can be applied to modelling scale-free network models, which, as it turns out, are characterised by small-world properties. This means, for instance, that members of the network only exhibit six degrees of separation, like most people in our society.

Revisiting the roots of a physics field known as computational statistical mechanics

It may sound like the stuff of fairy tales, but in the 1950s two numerical models initially developed as a pet project by physicists led to the birth of an entirely new field of physics: computational statistical mechanics. This story has recently appeared in a paper published in EPJ H, authored by Michel Mareschal, an Emeritus Professor of Physics at the Free University of Brussels, Belgium. The article outlines the long journey leading to the acceptance of such models - namely Monte Carlo and Molecular Dynamics simulations - as reliable evidence for describing matter. This happened at a time when the computing power required to run simulations was scarce. Today, these techniques are used by thousands of researchers to model the behaviour of materials, in contexts ranging from fusion to biological systems.

The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥106) accumulated in such a device may be ejected all at once, so as to generate an intense pulse.

New study outlines key factors affecting the transfer of molecules through biological channels

In our bodies, the transfer of genetic information, viral infections and protein trafficking, as well as the synthesis and the degradation of biomolecules, are all phenomena that require the transport of molecules through channels. Improving our control of these channels and the capacity of molecules to get across could have many potential applications in the fields of energy, biotechnology and medicine. These include ultra-fast DNA sequencing, detection of biological markers used in disease diagnostics, protein folding, high-resolution determination of the size of biological molecules or even the control of ion or biomolecule transport through the protein sensor. In a new study published in EPJ E, Manuela Pastoriza-Gallego from the University Paris-Seine, France, and colleagues have shown how to alter external factors, such as external voltage, to control the transport of a dextran sulfate molecule - a polyelectrolyte - through the nanopores of the aerolysin protein channel.

Example of raw images from the detector for identical particle operations with antiproton detection (left) and electron detection (right)

Improving the spatial compression of a mixed matter-antimatter trapped plasma brings us one step closer to grasping the acceleration of antimatter due to Earth’s gravity

An international team of physicists studying antimatter have now derived an improved way of spatially compressing a state of matter called non-neutral plasma, which is made up of a type of antimatter particles, called antiprotons, trapped together with matter particles, like electrons.

An open source software that is able to construct synthetic blood vessel networks in 3D, matching the properties observed in real tumor samples.

The tumor vasculature is a major target of anticancer therapies. Rieger, Fredrich and Welter at Saarland University, Germany have been pursuing a quantitative analysis of the physical determinants of vascularized tumors for several years [1]. With the help of computer simulations they have been able to recapitulate the knowledge accrued from in vitro research of tumor spheroids, animal models and clinical studies and have re-created a vascularized tumor system in silico.